KD seasonality shifts from winter to summer after COVID-19 pandemic

A 10-year study in Japan has found that the seasonality of Kawasaki Disease (KD) has not returned to the usual winter-dominant pattern even after lifting the COVID-19 infection mitigation measures.

The authors conducted a population-based retrospective survey among hospitalized patients with KD in Shiga Prefecture, Japan, from 2015 to 2024. They analysed monthly variations in KD incidence from 2021 to 2024 using the 2015‒2019 period as reference and examined the seasonality of 10 common paediatric infectious diseases and seasonal influenza during the study period.

Overall, 2,077 patients with KD were identified. During the implementation of public health measures against COVID-19 from 2020 to 2022, the incidence of KD remained low. Afterward, the incidence reached its peak (128.2 per 100,000 person-years) in 2023, along with the lifting of mitigation measures. KD incidence remained high at 118.9 per 100,000 person-years in 2024.

The traditional winter peak in KD incidence disappeared after 2020 and was instead observed during the summer of 2021‒2022 and in the spring of 2023‒2024. The number of patients infected with respiratory syncytial virus, which had had its highest during the fall and winter from 2015 to 2019, reached its peak in the spring and summer of 2021 onward.

“Continued surveillance is warranted to determine whether the winter-dominant pattern re-emerges,” the authors said.